The thought had popped into his mind sometime after the run in with The Pharaoh. The history book that Ladybug had dropped meant that she was his age at least. She may have denied it, but that could just mean that she was trying to avoid narrowing down who Ladybug could be. Then he started connecting curious coincidences. The Horrificator sealed the whole school, but somehow Ladybug was there to save the day. That meant that she had to be already inside the building. When that thought popped into his mind, he couldn't resist playing with it. Adrien had the curiosity of a cat. Especially when the thing he wanted to know about had anything to do with his lady.
Adrien was playing with the idea of going to school with his lady just as he got out of chemistry class (which he was extremely late to) Nino was walking with him to the library to get some studying in (for chemistry because… absences) when something his best friend said that snagged him out of his thoughts.
"Wha? What did you just say Nino?" Adrien suddenly gave his friend all of his attention.
"Huh? That we should have a study group with Marinette and Alya?"
"Before that?!"
"That you need to stop skipping chem?"
"After that!"
"That you and Marinette should study together because you are both either always absent or late?"
"Yes! You are a genius! We should ask her… them." Adrien felt himself getting excited. Marinette was brave, and sweet. She also had black hair and blue eyes. If she missed what he missed in school, that could mean that she was busy fighting crime alongside Chat Noir. It all fit. Was prying okay though? He couldn't help it if he just figured it out right? Also, how in the world had he not thought of this sooner?!
"Study together!? I love books! I mean books have pages and you read them and studying is how you use them but sometimes you just read them for the fun of it…" Marinette abruptly stopped talking with a soft kick from Alya. She grinned widely and just gave him a thumbs up.
"Yeah that sounds cool. Maybe over lunch break tomorrow?" Alya recovered the conversation for her silly best friend who always fumbled over words in front of Adrien.
Adrien just nodded. Ladybug never ranted or stuttered. She was so confident and she always had a plan. Still, he couldn't write Marinette off yet. There were too many similarities. Plus, it wasn't like the Adrien that everyone knew acted like Chat Noir. He had more courage and self-expression as Chat Noir, so maybe Ladybug had more confidence as Ladybug. It both bothered him greatly and gave him great satisfaction to think of that. On one side, it meant that there were still so many sides of his love that he had never seen. But on the other, it meant that he was better acquainted with her secret side than anyone else.
After school, Adrien spent more time than he should on Alya's blog again. He felt closer than ever before and he really hopped that he wasn't wrong. He desperately wanted to know everything about Ladybug. He saw her every day, but she was so far away from him.